The Musical Notes are 12, 7 being natural and the other 5 are altered.

The natural notes, sorted out by their pitch, from the lowest to the highest, are: C, D, E, F, G, A and B. These 7 notes form the so called C Major Scale and correspond to the “white keys” in the piano. After the B comes another C and so on. Nevertheless, the first and second C are not identical, as the latter is higher than the former. The thing is that, from the point of view of Physics, the “vibration frequency” of the second C is exactly double that of the first C, which makes those notes very “affine” when hearing them, to the extent of assigning them the same name. It is said that the distance between them is one octave, because there are 8 natural notes from the first to the second C, including both the initial and the last note in the count.

The distance between two consecutive natural notes are not always the same, for in some cases the distance is one Whole step (W) and in others it is one Half step (H). Particularly, between E and F there is one half step, as well as between B and C. On the contrary, between any other two consecutive natural notes there is one whole step. This is the reason why the so called altered notes are placed between them, at a one half step distance, and they correspond to the “black keys” in the piano (Fig. 1). Therefore, a set of 12 different notes is obtained, there being one half step between any note and the next one. Thus, the distance between a given C and its octave (that is, the next C) is 12 H or 6 W. This set of 12 notes is known as the Chromatic Scale.

Figure 1. The musical notes and their location in a piano.

In order to name the altered notes, the accidentals are introduced, which are the sharp () and the flat (). The sharp raises the natural note one half step and the flat lowers it one half step. Thus, for example, between C and D (where there is a whole step distance) an altered note is placed, which can be called C or D. These two notes, corresponding to the same pitch but having different names, are called enharmonic. In the same way, E and F natural, or B natural and C, are also enharmonic (the term “natural” means “without any accidental”). Occasionally, the double sharp () and the double flat () are used to raise or lower the natural note one whole step, respectively.

In spite of the fact that the 12 notes are uniformly spaced, in Fig. 2 the different consideration given to the natural and the altered notes is evident, as well as the lack of uniformity in the distribution of whole and half steps among the natural notes. All these things, which seem to be strange and whimsical, are in fact the result of centuries of evolution of Music Theory, which in turn is the consequence of the affinity relationships that exist among sounds, along with the strong cohesion and unity that the set of 7 notes composing the Major scale have. All these questions will be properly explained in different chapters.

Furthermore, as will be shown in Chapter 5, a Major scale can be built beginning with any of the 12 notes, thus obtaining, for example, the D Major scale, A Major scale, etc., what makes the 12 notes equally important. The C Major scale is, simply, the one having exclusively natural notes. In the Guitar, for example, the 12 notes are given exactly the same treatment (Fig. 2).